Oxygen is the most common drug used in the critical care of infants. There is significant morbidity and mortality associated with excess or inadequate levels. For this reason, an important element of many therapeutic interventions in the ICU requires assessment of their acute impact on oxygenation. It is common to normalize the arterial level of oxygen with the fraction of inspired oxygen (PF-ratio). Further, a change may often be more important than the absolute level. Though the PF-ratio is often reported, it was surmised that the rarely reported, relative magnitude of change in PF-ratio might be a useful metric for assessing the stability and effectiveness of therapy. Therefore, individual patient data from two different studies were evaluated. The cases included periods of therapeutic intervention and periods without intervention, thus permitting the evaluation of the PF-ratio's potential sensitivity to change and thresholds for relevant change. During surfactant administration in extremely preterm infants, the PF-ratio improved at least 25% in 91% of the infants, while 9% showed less than a 10% change. During high-frequency oscillatory rescue in children, the PF-ratio improved at least 25% in 76% of the infants, while 8% showed less than a 10% change. Consideration of thresholds of 50% and 5% reflected low prevalence. In periods of routine care, the prevalence of marked changes was less prevalent but still common (6% and 55%) and periods of little change more prevalent (21% and 21%). We believe this initial work supports the feasibility of using the magnitude of change in PF-ratio and provides a useful stimulus for additional evaluations.

Department of Biomedical Technology Faculty of Biomedical Engineering Czech Technical University Prague Kladno Czech Republic

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